I have opened a case with support team and they provided me the below work around.
Stop AdminUI if running
Take backup of existing api-doc.war from folder <AdminUI_Install>\standalone\deployments\iam_siteminder.ear
copy extracted api-doc.war to folder <AdminUI_Install>\standalone\deployments\iam_siteminder.ear
Start AdminUI
Click RestAPI URL.
I am not sure how I can attached new .war into this response.